It is frequently necessary to place, remove, or repair an electronic surface mounted component on a printed circuit board (PCB). Electronic components are typically bonded to the PCB with a solder material that has a melting point above the maximum operating temperature of the component, but sufficiently low so that only a small quantity of thermal energy is needed to melt the material. Thermal energy can be transferred via conduction, such as by a soldering iron; via convection, by means of forced hot air; or via radiation, as provided by an infrared lamp, for example.
It is known to apply a stream of hot air or other chemically inert gas to provide localized convective heating of the leads of a component. For example, a typical surface mounted component is square or rectangular, with leads that project outwardly from each of its four sides. If the component is square, a round region of hot air or hot gas centered on the component must be large enough to include the leads so that they receive direct exposure to the hot air. However, if the region is large enough to heat all of the leads, then the component is exposed to an excess of thermal energy, the excess energy potentially damaging the component. Also, the hot air undesirably heats up surrounding areas of the PCB and neighboring components. This not only may damage adjacent components but also may ultimately result in warpage or delamination of the PCB. An analogous problem arises when a round region of infrared illumination impinges upon all the leads of a component; the region necessarily includes the component itself, possibly causing damage to the component. Also, adjacent components can be damaged as well due to over heating and possible melting of their solder joints.
It is also known to supplement the above infrared heating with forced hot air or hot gas directed towards the location of the component from a position under the PCB to provide preliminary conductive heating to the component. However, since surface mounted components are commonly found on both sides of a PCB, this method of heating can result in overheating and damage to the components exposed to the forced hot air.